North Korea conducted its third underground nuclear test today, defying repeated international warnings and sanctions. The North Koreans called the test a response to reckless hostility from the United States. The White House called it highly provocative. And the U.N. Security Council scheduled a meeting this morning.

For more on the story, we turn to NPR's Frank Langfitt, who's reporting from Shanghai. Frank, North Korea had said that it was going to go through with this test no matter what. What's the significance of the fact that they actually did it?

FRANK LANGFITT, BYLINE: Well, this is the third nuclear test they've done in about six years. And one of the things that North Korean state media mentioned was it was smaller and lighter than earlier devices. And what they seem to be suggesting is that they may be making progress towards putting together a nuclear device that you could actually put on a missile. If you remember, back in December, they had a satellite launch. Most people thought that was actually ballistic missile test.

So it's pretty clear that they're headed in this direction and they're trying to kind of get that message out there. Obviously the things that North Korean media say, there's no way for anybody to independently confirm other than there was a test.

WERTHEIMER: Frank, what about the timing? What are you hearing about North Korea's thinking on doing this now?

LANGFITT: Well, you know, the main external audience for this is often the United States. And Kim Jong-un, the leader of North Korea, seemed to time it to try to upstage present Obama's State of the Union. You've got to remember the relations between these two countries are really quite bad, have been so for decades.

U.S. fought a war with North Korea in the 1950s. There was never a peace. It's actually an armistice. And North Korea sees the U.S. as kind of its biggest threat. After that ballistic missile launch back in December, the U.S. pushed for new U.N. sanctions against North Korea. And this test looks like it's sort of continued push-back from North Korea.

WERTHEIMER: So what do you think is the political message North Korea's trying to send?

LANGFITT: Well, you know, not only are they sending out a message to the outside world but they're also speaking to their own domestic audience. And you have a new young the leader in North Korea in Kim Jong-un, and he seems to be trying to show his mettle. People had hoped that he would be less belligerent, at least near outside countries. But there is a long militaristic tradition in the country and he seems to be following it.

Also, it's worth remembering that on Saturday - this coming Saturday - is Kim Jong-un's dad's birthday, the former leader of North Korea, Kim Jong-il. So this may also sort of be timed to his dad's birthday.

WERTHEIMER: We appear to be learning a few things about what North Korea can do now. Does this weapons program threaten North Korea's neighbors or maybe even the United States?

LANGFITT: Well, certainly not the U.S. now. They still don't have the ability at all to put a nuclear device on the top of a - you know, inside a missile. And no one thinks that they would attack Japan or the United States, because the retaliation would be overwhelming.

But I think some analysts are concerned that if North Korea does have this capability, eventually that it could get just more aggressive with its neighbors, that it's going to be more confident and might push around its neighbors more. You remember, back in 2010 it actually sank a South Korean naval vessel. And so I think the neighbors and the United States don't want to see more of that.